Windows 7: Incoming packets dropped, RTL8100C, Windows 7 32-bit

First of all, I'm not sure if this should be here or if it should be in the Hardware & Devices subforum, so if I have it in the wrong place you will have to excuse me. Anyway...
I have an oldish eMachines computer here that I'm trying to set up as a file server to replace an old S939 Athlon box. However, the NIC on it, a Realtek RTL8100C, seems to like dropping incoming traffic. RDP will stop responding, FTP transfers will die, and SMB stuff will take forever to get directory listings. I did a ping -t on the machine and I keep getting "Request timed out." regardless of what machine I am pinging from or where the eMachines is plugged in (router upstairs or switch in the basement.) However, here's where things get interesting. If I run a ping -t to the router FROM the eMachines, suddenly requests stop timing out when pinging the eMachines from another computer. Also, when booted into Parted Magic from a CD ping requests do not drop, nor do they drop when using a Windows XP-based WinPE disc. I have tried updating the driver from Realtek's site and from Windows Update. Any ideas?

For reference, the exact model of eMachines is W3653a with an Elitegroup 945GCT-M3 motherboard.

It sounds like a bad driver. You could try older drivers or buy a new NIC.

Oh, I forgot to mention that when I tried a PCI ethernet card I had the same issues. I also just reinstalled Windows 7 again and it's still doing it.

Do packets fail in the safe mode?

I assume you mean Safe Mode with Networking as Safe Mode just gave host unreachable errors. In Safe Mode with Networking I don't get any ping replies at all.

EDIT: I just had to log on, doh. I'm getting no packet loss whatsoever while in safe mode with networking.

Yes - safe mode with networking...

So, work thru a clean boot:
Troubleshoot Application Conflicts by Performing a Clean Startup

What antivirus/security suite are you using?

None, like I mentioned I just reinstalled the OS. Nothing else has been installed, not even updates.

Did you use an OEM OS DVD to re-install W7?

Or maybe a retail OS DVD?

It's a retail one I slipstreamed some updates and SP1 into, but I can try with a retail disc tomorrow.

Sorry for the late response, but I had some things come up here. I tried again with a retail disc but with the same results.